Prevalence of Demodex in Association with Ocular Signs and Symptoms: Evidence from a Large Population of Male Soldiers Living in Garrison

Background: The Demodex mite is the most common ectoparasite on human skin. It’s a matter of debate whether this colonization should be an area of concern and can cause pathologic consequences or, in contrast, Demodex should merely be considered as an innocent saprophytic organism living on the skin. Objectives: We aimed to evaluate the prevalence of ocular Demodex infestation in a large population of male soldiers with a similar range of age, in whom we expected a high transmission rate due to environmental factors and close contacts. Besides, we evaluated the correlation between Demodex and ocular clinical manifestations. Methods: In total 903 soldiers living on a military base in Iran were enrolled in this epidemiological cross-sectional prevalence study conducted in the summer of 2020. Data were collected using a questionnaire on ocular symptoms, and participants were assessed for the presence of Demodex spp. Results: A total of 904 males with a mean age of 21 ± 2 years (ranging from 19 to 25) were included. The overall prevalence of Demodex infestation was 77.2% (86.8 and 26% in patients with and without blepharitis, respectively). Of 698 patients who were positive for Demodex, 58.6% reported eye discomfort, whereas it was experienced by 23.9% of Demodex negative participants, the difference was statistically significant (P-value < 0.001). Conclusions: There is a strong association between the prevalence of Demodex spp. and symptoms, in particular itchy eyes. However, some patients are asymptomatic. This finding supports the notion that the number of mites may be important concerning the manifestation of clinical signs of blepharitis; however, the role of Demodex spp., as a commensal, should not be overlooked. Treatment should not be aimed at full eradication of the mite but rather restoring the ocular ecology to a balanced state.